WIP: Add detailed help.

[ntadimeti]

Add detailed help to command line options. This will prevent the need to add extra documentation somewhere else.

[ntadimeti]

@avantikalal and @tijyojwad can you tell me what options need highlighting ? From a quick glance, the current help looks pretty self explanatory to me.

[tijyojwad]

@ntadimeti check out https://docs.python.org/2/library/argparse.html#sub-commands . The subparser concept can be used to better organize the help messages between train, eeval and infer

[ntadimeti]

Will open a fresh PR that re-organizes the commands. Avantika has another PR that adds help where needed.